Factors influencing acute loss of lung compliance remain obscure. This project undertakes the study of one model of stiffening, as produced by hyperventilation of excised and in vivo lungs. The influence of temperature, amount of tissue hydration, end-expiratory level, tidal volume, and respiration rate are being explored. Mild degrees of interstitial edema are clinically common and precede the more severe forms involving alveolar filling and foam production. The mechanisms which are at work during the transition period, including alterations in the mechanics of the interfacial lining, are under investigation. Correlations with N2-based pulmonary function tests are included. Neural influences on surfactant synthesis, release, and properties, and on fluid transudation in the lung are presently poorly understood. Studies to be conducted include effects of both sympathetic and parasympathetic nerve stimulation. BIBLIOGRAPHIC REFERENCES: In Press, Hoppin, F.G., Jr. and J. Hildebrandt. Mechanical properties of the lung, in "Bioengineering Aspects of Pulmonary Biology", J.B. West (Ed.), Lenfant Series, 1976. Nagao, K., R. Ardila and J. Hildebrandt. Tissue fluid and the loss of surface activity from excised rabbit lungs. Fed. Proc. 34:426, 1975.